The idea that pāsāda means “multi-storied building” or “palace” is taken from the commentaries. In the Canonical texts, however, pāsāda seems to be a generic term for a stilt-house. I have personally researched this term and written a short essay, here, to substantiate my translation.
As for hammiya, there is not enough evidence on the suttas/vinaya to ascertain its precise meaning. For this reason I have followed the commentarial suggestion that it is a specific type of pāsāda. Since the allowable zones around the two buildings are the same, I have not made a separate category for hammiya, but included it under pāsāda.
I hope this makes sense.